External resonant section tubes



Oct. 27, 1959 R. J. BONDLEY 2,910,614

EXTERNAL RESONANT SECTION TUBES Filed Sept. 3, 1957 In ve rvtcr: FPa/ph J Bond/e United. States Patent 2,910,614. EXTERNAL RESONANTYSECTIQN TUBES Ralph J. Bondley, Scofia, N.Y., assignor to General My invention relates to improvements in electron tubes having resonant sections with portions external to the evacuated tube envelope.

Many tubes have resonant sections that are diflicult to tune because the frequency determining means for the sections are contained within the evacuated tube envelope. To overcome this difiiculty, tubes have been developed having portions of the resonant 'sections' external to the evacuated envelope so that the frequency determiningmeans such as plungers, diaphragms, or the like, can operate outside of the envelope in these external por tions.

In these prior external resonant section tubes, ceramic cylinder insulators-called windowsprovide the air seal between the evacuated and non-evacuated portions of the resonant sections. Because these cylinders are neca essarily close to the tube electron beam, they are subjected to bombardment by stray electrons, X-rays, gas ions, and the like, that produce local heating and subsequent deterioration of the cylinders. Obviously, the resulting failures could be diminished if less insulator surface were subject to bombardment.

' Accordingly, anobject of the present invention is to provide an external resonant section tube having minimum window area exposed to the electron beam.

The windows in some prior external resonator section tubes provide physical support for the tube as a unit, and accordingly are made thick for strength. But thick windows are disadvantageous from a local heating viewpoint, because the amount of heat generated by dielectric loss is proportional to the volume of the windows. Further, thick windows produce a relatively large discontinuity in the resonator sections and also introduce un desired capacitance.

Therefore, another objectis to provide an external resonatorsection tube having thin windows.

If the window and the metal to which it is sealed do not have the same thermal coefficients of expansion, the metal immediately proximate to the windows has to be thin with the result that as it expands due to heat, it does not have suflicient strength to break 'the windows. In a tube having a cylindrical window, this thin metal corn- Pl tely encircles the tube and thus is a portion of the main tube support. Consequently, these tubes are weak and often bend axially thereby causing misalignment of the drift sections along the tube axis.

Thus, a further object of the present invention is the provision of an external resonator section tube in which relatively strong thick metal provides the axial support for the tube.

The above-mentioned objects are achievedin one form of my invention by the provision of a klystron with an elongated evacuated envelope having an electron gun at one end and a collector electrode at the other end. The central portion of the envelope is comprised of a plurality of axially disposed drift sections separated by gaps. At each gap there is an individual cylindrical cavity resonator having a short center section transversely arranged 2,910,614 te e O t- 5 1959 ICC 2 to and extending between the drift sections on either side cf the respectivegap. At one or both ends of each center" section'thin disc-shaped windows provide vacuum sealing and extending external cavity resonator portions complete the resonator} Tuning pistonsmounted in the external cavity-;resonator portions provide conveniently accessiblefexter'nal tuning. l v l l i Although the specification concludes with claims particularly pointing out and distinctly claimingthe subject matterthat I regard as my invention, the'invention may be better understood from the following description considered in connection with the accompanying drawing in which: l i

Fig. 1 is a side view, partly embodiment of my inventionf Fig. 2 is a cross-sectional view of my preferred embodiment alongthe line 22of Fig. 1'; and

Fig. 3 is a cross-sectional view taken along the line 33 of Fig. 1. In the several figures of the drawings, corresponding elements have been indicated by corresponding reference numerals to facilitate comparison. Referring specifically in section, of a preferred to Fig. 1, the illustrated electron tube comprises an elongated envelope having an electron gun 11. at one'end and number of resonators.

Electron gun '11 includes a dish-shaped cathode 25' mounted within a focusing electrode 26 and heated by a coil 28 secured by two insulating beads .29 in a panshaped element 31. Element 31 is separated from an oppositely disposedannular ring 32; by a cylindrical insi lating member 34. i s V I At the opposite end of the envelope, collector 12 00mpr'ises a hollow cylindrical member'SS. The means for cooling collector 12, which may be a conventional water jacket, has been omitted in order to simplify the illustration. For the same reason, s'tructure that may be conventional has not been shown for producing a mag netic field between collector 12 and gun 11.

Resonator 22 comprises a cylindrical short center section 36 across the open ends of which two disc-shaped low-loss windows 37 are vacuum sealed. These windows can be constructed of fused quartz, a ceramic, or any one of a number of other suitable materials. An airftiglitseal between these windows and section 36 is needed because the center portion of the tube including thekd rift sections, is evacuated. Two external cylindrical cavity resonator sections are'joined to the ends of section 36 by means shown to berigid, but that could be detachable, such as spring'contact fingersl Frequency determining means here illustrated as twp pistons 40, that can be slid for tuning by means of'rods 41, are in slidable electrical engagement with the inner wall of sections 39 through a plurality of spring finger contacts 42. Of course, other frequency determining means such as a bellows or a diaphragm could be used instead of pistons 40. The input to resonator 22 may be provided by any suitable means such as a wave guide with an opening into the resonator or a coaxial line with a probe or a coupling loop extending into the resonator. The means shown comprises a coaxial line having an outer conductor 43 and an inner conductor 44 separated by an insulator spacer 46. Conductor 43 extends into resonator 22 in the form of a loop. Of course, the size and position Although the circular symmetry of resonator 22 is preferred from ,a conjstruction consideration, the resonators can be of other tube-like shapes, as is illustrated by the rectangular cross-sectional shape of resonat r 23. This resonator has a four-sided short center section 47 extending between and supporting the drift sections and 17. At the ends of section 47 there are two vacuum sealed windows 49 and two coaxial, rectangular cavity resonator sections 50. Tuning of resonator 23 is provided by two rectangular pistons 52 that are slidable in sections 50 by means of rods 53. Electrical contact be tween sections 50 and pistons 52 is maintained by means of spring contact fingers 54 Energy, if small, can be coupled out of resonator 23 by means of a loop suchas is shown with resonator 22. But in most applications .the energy will be large enough to' require a waveguide output and thus a wave guide 56 is shown having an opening into resonator 23. The size and position of this opening will be determined by the required matchmg.

The cross-sectional view of Fig. 3 shows the support given by section 43 to drift sections 15 and 17. Any tendency for these drift sections to move out of alignment is resisted by section 43 alone. Windows 49 do not provide any significant structural support but rather serve only to provide an insulated air seal for resonator 23. r

The operation of the disclosed tube is conventional. That is, the input wavefro'm the coaxial line excites resonator 22, which is tuned to the wave frequency. An electric field is thereby produced across gap 19 that affects the velocity of electrons-emanating from Igun 11 as they passthrough this gap. When the lower end of this gap is positive with respect to the upper end, the electrons'then presentini the gap are accelerated positively, and during a reverse condition the electrons in the gap are accelerated negatively. The differences in acceleration produce differences in the velocities of'the electrons so that as they pass through drift section 15 they tend to bunch because the fast moving electrons from a positive half cycle of the voltage across gap 19 catch up with the slow moving electrons from the previous negative half cycle. These bunches will thus arrive at gap 20 a time apart equal to a period of the input to resonator 22. Resonator 23 is tuned to the frequency of this input so 'that these bunches excite resonator 23, causing an amplified wave to be produced therein. This wave is coupled to the utilization device by wave guide 56.

The manner in which the disclosed structure provides the mentioned objects should now be apparert. Because the short center sections 36 and 43 of resonators 22 1 q he and 23, respectively, surround all but a small fraction of the area around gaps 19 and 20, respectively, windows 37 and 49 are subject to much less bombardment than if they were cylindrically situated around these gaps as in the prior external resonator section tubes. Also, because these windows do not bear any significant structural support, they can be constructed of thin material and thereby can diminish local heating due to dielectric loss and discontinuity in the resonant section due to thepresence of the dielectric. Further, the disclosed tube is rigid because much of the structural support. is provided by metal that is not immediately adjacent the windows and thus that can be made thick and thereby very. strong. From the above it should be evident that the disclosed tube is not only subject to less window failures, but is mechanically more rigid than the prior tubes with the result that the drift sections remain in alignment.

Although the invention has been described with respect to certain specific embodiments, it will be appreciated that many modifications and changes may be made by those skilled in the art without departing from the spirit of the invention. I intend, therefore, by the appended claims, to cover all such modifications and changes as fall within the true spirit and scope of the invention.-.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An external resonant section tube comprising an electron gunfor emitting electrons, a collector electrode spaced from said electron gun for receiving electrons from said electron gun, a plurality of metallic drift tube sections extending axially between said electron gun and said collector electrode and spaced to produce a gap, a resonant section positioned to bridge the gap between two adjacent of said drift sections, said resonant section comprising a tube-shaped metallic center section rigidly extending between said two adjacent drift, tubesec: tions with the axis thereof transverse tothe axis of.said drift tube sections. 1

2. The external resonant section tube as definedLin claim 1 and including two dielectric windows'vacuum sealed respectively to opposite ends of said center section. 3. In an external resonant section tube, an elongated envelope comprising a plurality of axially-arranged metal-- References Cited in the file of this patent UNITED STATESPATENTS v 2,383,343 Ryan Aug, 21, 1945 2,450,026 Tomlin Sept. 28,1948 2,619,611 Norton et al. Nov. 25, 1952 2,629,066 Eitel et al. Feb. 17, 

